General Description

Wood bison are one of two subspecies of modern American bison. They have a dense coat of soft, warm, durable hair that is not hollow like moose caribou and sheep, but has a feel more like human hair. The hair is dark brown to black along the legs and lower body, to light brown along the hump. They begin to lose their winter coat as temperatures warm in the early spring. By mid-summer it is completely shed and has been replaced with new hair. They have curving horns that point upward and hair on their chin that resembles a beard. Their head and shoulders are large compared to their hindquarters. The wood bison's hump slopes almost straight up from the neck a pronounced hump ahead of the front legs. From there it slopes downward to the hips. The bone structure of this giant, forward hump has evolved in the Northern wood bison to support massive forward muscle structure that helps them sweep through deeper northern snows with their head to access grasses and sedges in winter. Adult males are approximately 6 ft tall at the shoulder, 10 feet long, and weigh over 2,000 pounds. The females are smaller, generally weighing around 1,200 pounds.

Similar Species

Plains bison (B. bison bison) are the other subspecies of American bison. Wood bison have a similar appearance to plains bison. Wood bison are on average about 15% heavier than plains bison. A wood bison's hump is taller and has its highest point forward of the front legs. The wood bison has woolly hair along its ribs where plains bison have very short hair. The hair of the Wood bison's beard, throat latch, ventral neck mane, chaps, and penis tuft are much less developed than that of plains bison. Wood bison have different vocalizations that plains bison, and wood bison's social interactions during the rut tend to be less violent than plains bison. All of these differences can be explained through wood bison's adaptation to the northern environment of grassy pockets of habitat within the sea of Northern forest where temperatures can be quite cold and snow can be deep for extended periods.

Life History

Reproduction and Growth

Female wood bison are sexually mature around 2 years old and can have their first calf when they are 3. They generally have
a single calf twice every three years. Wood bison are pregnant for 9 months and give birth from April to August with most
calves born in May. Newborn calves are red in color, similar to moose calves. In order to evade predators, calves can stand
within 30 minutes of birth and can run and kick within hours. After a week, calves will begin grazing but continue to nurse
for several months. After 10 weeks, their coats begin to darken and become dark brown by about 15 weeks of age.

Feeding Ecology

Wood bison are primarily grazers and mainly eat grasses, sedges, and forbs. They can use a variety of other plants; for example,
silverberry and willow leaves make up part of their summer diet. Wood bison graze in meadows, around lakes and rivers, and in
recent burns.

Behavior

Wood bison live in groups of up 20 to 60 animals during most of the year, but adult bulls usually live in smaller groups and
stay separate from the larger groups of cows and young bison except during the breeding season in late summer. They have strong
social bonds and like to be near other bison.

Movements

Bison generally remain within a home range but move between seasonal ranges, and move each day from meadow to meadow, where
they graze and rest before moving on. Although bison move slowly when feeding, they are capable of moving rapidly over long
distances. The size of their year round range tends to increase with population size, and also depends on habitat quality. In
lower quality habitats they will move over a larger home range.

Range and Habitat

Wood bison once ranged across northwestern Canada and were also found in a large region in Interior and Southcentral Alaska. Alaska’s population was extirpated by the early 1900s, although several small herds persisted in Canada.

In 2015, 130 wood bison were released to the wild along the Innoko River near the community of Shageluk. About 16 wild born calves were recruited into the population in the summer of 2015. As of October 2015, the core range of these wood bison, known as the Lower Yukon/Innoko Rivers Herd, was within 30 miles of Shageluk, except for two lone bison that have explored habitats along the Yukon River from Russian Mission to Galena.

Status, Trends, and Threats

Status

As of October 2015, Alaska’s wild wood bison population numbered between 120 and 130 animals. In 2015, 130 wood bison were released to the wild along the Innoko River near the community of Shageluk. Over the course of the first six months in the wild, there were some births and deaths. Biologists think 400 to 500 animals is a good minimum number for long-term genetic diversity for the Lower Yukon/Innoko rivers herd. Over time, the surrounding habitat could potentially accommodate as many as 1,000 to 5,000 wood bison.

As of October 2015, there were 16 wood bison in captivity at the Alaska Wildlife Conservation Center. These animals are expected to remain at the Center for educational purposes.

The original source of the wood bison reintroduced in Alaska was a disease-free herd in Canada. Currently, habitat in Canada supports about 4,700 wood bison in six healthy, free-ranging herds. A similar number of wood bison occur in herds that are infected with cattle diseases in the area of Canada's Wood Buffalo National Park (WBNP). There are also herds of domesticated wood bison in Canada. In the United States, the wood bison is listed as threatened under the Endangered Species Act (ESA). To learn more, visit the ADF&G Special Status page for wood bison.

NatureServe: Global – G4T2Q (Imperiled)

ESA: Threatened

Population Trends

Wood bison were the last bison to occur naturally in Alaska but disappeared during the last few hundred years presumably because of unregulated hunting and changes in habitat distribution. By 1900, there were fewer than 300 individuals remaining in Canada. By 1950, it was thought that wood bison no longer existed as a subspecies. In the mid 1950's, a small remote herd of wood bison was discovered,and in subsequent years, many were captured and moved to Elk Island National Park where they have kept free of disease and propigated to be source animals for disease free wood bison herds throughout their former range and in Siberia. Canada has put considerable effort into the conservation and management wood bison. As of May 2013, there were approximately 11,000 wood bison in Canada, including nearly 5,000 in 7 free-ranging disease-free herds; 6,000 in 5 free-ranging but diseased herds; and 300 in the Elk Island park captive population that is maintained to provide stock for conservation efforts.

The wood bison management plan calls for growth of the Lower Yukon/Innoko rivers herd. Population models suggest that the 130 animals reintroduced to the wild in 2015 could grow to about 250 by 2021 and to 500 by about 2030, based on growth observed in populations reintroduced to areas of Canada in recent decades. Biologists are closely monitoring how the newly reintroduced bison are responding to their new habitat.

Threats

Loss of Habitat is the main threat to most wildlife. Alaska has thousands of square miles of unoccupied bison habitat, ready to accommodate bison. Disease is an issue in Canada, but the cattle diseases that some bison have there have never been detected in Alaska. Predation could someday be an issue, but for all of the reintroduced wood bison populations in Canada, and the plains bison populations in Alaska, predators took decades to figure out how to kill them effectively, and predators still have little effect on disease free bison populations like they do on moose, for example.

Fast Facts

Size
Males — 2,000 lbs; females — 1,200 lbs.

Lifespan
20 years

Distribution
Canada, with one wild herd in westcentral Alaska, the Lower Yukon/Innoko Rivers Herd near Shageluk